It's going to be a very long and slow process. I am able to get him out of his cage if he's 'in the mood', if you know what I mean. Once he's outside his cage, it's as if a switch has been flicked on, and he immediately becomes very anxious, quivering the shoulder portion of his wings.
Near his cage he's a velociraptor. Away from his cage I can at least hold him for a bit before 'the bite' happens.
I finally heard the very first phrase he's ever uttered: 'Hey stupid'. 😞 Not surprised.

You can tell by looking at the feather's shaft as to whether it was barbed off or not. If the tips look chewed, and you know he didn't chew them after the fact, then likely it's plucking. The tips from those feathers at the top of your picture look like they were naturally molted.
Do you see any bald areas on his body?
I'm thinking that it's likely a heavy molt.

I agree with Neoow regarding no shoulder time if he's a biter.
It's all about learning to read their cues. My new rescue bites whenever he's on or near his cage. He was cage bound for 8 years, so he's extremely cage protective. Once he's away from his cage, he's very anxious, so I must make all movements slowly so as not to frighten him. I will not pet him yet. For now it's all about getting him used to perching on my hand. Once he's completely comfortable with that, I will watch his eyes and feathers for signs that it might be the right moment to introduce stroking and petting.
Again, it's all about Grey time. If you can't respect their time, you and your family will get bit. Simple as that.

There is absolutely no guarantee that Rudy will accept another bird. I have 12 birds, and only a few get along. If you decide to get another one, you need to go in with an open mind that he might not connect with him.

For us, with 12 birds, it's all about structure. They know when they're going to be fed, what time of day they'll be let out of their cages, in what order they'll be coming out, and when I'll be interacting with them one-on-one. It's incredible how they've learned to expect what's up next.
Since they're all flighted, and not all of them get along, they're let out in 'get along' groups. They even know when, and in what order I'll be returning them to their cages, and will usually head back inside on their own when they see the order.
Birds truly are intelligent little beings!